Synthesis of echinocandin antifungal agent

ABSTRACT

The present invention relates to echinocandin cyclopeptides and to methods for preparing echinocandin cyclopeptides.

BACKGROUND

This invention features methods for the synthesis of compounds usefulfor treatment of fungal infections and conditions related thereto.

Fungal infections, such as those caused by Candida and Aspergillus, canbe serious and life-threatening infections that represent a significantpublic health issue, particularly in highly vulnerable populationsincluding the elderly, post-surgical, critically ill, and otherhospitalized patients with serious medical conditions. Because ofincreasing resistance to existing antifungal drugs, there is an urgentneed to develop new and more effective antifungal agents to treat theseserious infections. Echinocandins are members of a leading class ofantifungal agents for the treatment of fungal infections. Thesecompounds target the cell wall by preventing the production of1,3-β-D-glucan through inhibition of the catalytic subunit of1,3-β-D-glucan synthase enzyme complex.

Although nature can provide a substantive part of the complex chemicalstructure of semisynthetic cyclopeptides, and in many cases having allchiral centers in the required configuration, the subsequent chemicalconversions into the therapeutically active derivatives neverthelessoften require unprecedented approaches. Usually the structures inquestion are chemically unstable and/or prone to racemization and simplydo not allow for otherwise obvious synthetic manipulation taught insynthetic organic chemical textbooks. This chemical instability is evenmore pronounced in anidulafungin, caspofungin, and micafungin due to thepresence of the notoriously fragile hemiaminal or aminal moieties. Theproduction of pharmaceutical grade echinocandins is complicated by thedifficulty and expense of relying upon chromatographic methods to removestructurally similar impurities produced in the course of the commercialscale production of these antifungal agents.

There is a need for convenient synthetic alternatives that permit thecommercial scale production of semisynthetic echinocandins. Theseapproaches can be useful alternatives to existing synthetic methods andcan achieve a higher yield, higher isomeric purity, elimination of amutagenic impurity, a reduced waste stream, or any combination of theabove.

SUMMARY OF THE INVENTION

The invention features a method of synthesizing compound 1, the methodincluding the steps of: (a) providing a first composition including aboronate ester of anidulafungin; (b) providing a second compositionincluding a salt of choline; (c) combining the first composition, thesecond composition, and an acid to form a mixture, wherein the solventsystem is selected to form a precipitate of a reaction product havingformula (I):

where X⁻ is an anion; and R is C₁-C₆ alkyl, C₃-C₁₀ carbocyclyl, C₂-C₆alkenyl, C₆-C₁₀ aryl, or C₂-C₉ heteroaryl; and (d) hydrolyzing thecompound of formula (I) to form compound 1, or a salt or neutral formthereof.

In some embodiments, R is C₁-C₆ alkyl or C₆-C₁₀ aryl. In someembodiments, R is C₆-C₁₀ aryl. In some embodiments, R is substituted orunsubstituted C₆ aryl.

In some embodiments, the concentration of the mixture is at least 0.01,0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1 moles per L(e.g., from 0.01 to 0.03 moles per L, from 0.03 to 0.05 moles per L,from 0.05 to 0.1 moles per L, or from 0.1 to 0.2 moles per L) relativeto the compound of formula (I). In some embodiments, the concentrationof the mixture is at least 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45,or 0.5 moles per L (e.g., from 0.1 to 0.3 moles per L, from 0.2 to 0.4moles per L, from 0.3 to 0.5 moles per L, from 0.4 to 0.6 moles per L,or from 0.5 to 0.7 moles per L) relative to the compound of formula (I).In some embodiments, the concentration of the mixture is at least 0.5,0.6, 0.7, 0.8, 0.9, or 1.0 moles per L (e.g., from 0.5 to 0.8 moles perL, from 0.6 to 0.9 moles per L, from 0.7 to 1.0 moles per L, from 1.0 to1.3 moles per L, from 1.0 to 1.5 moles per L, or from 1.5 to 2.0 molesper L) relative to the compound of formula (I).

In some embodiments, step (c) includes a solvent system that includesacetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran,1,2-dimethoxyethane, cyclopentylmethyl ether, or tert-butyl methylether, or mixtures thereof. In some embodiments, step (c) includes asolvent system that includes a mixture of tetrahydrofuran andacetonitrile. In some embodiments, step (c) includes a solvent systemthat includes a mixture of 2-methyltetrahydrofuran and acetonitrile.Optionally, the solvent system further includes trifluoroaceticanhydride. In some embodiments, the solvent system contains from 0.1% to5% (w/w) water. In some embodiments, the solvent system is anhydrous.

In some embodiments, step (c) includes combining at least 10, 15, 20,25, 30, 35, or 40 molar equivalents (e.g., from 10 to 80, from 10 to 40,from 20 to 60, or from 20 to 40 equivalents) of the salt of choline andat least 1 molar equivalent of anidulafungin, as its boronate ester.

In particular embodiments, step (c) is performed at a temperature ofless than 40° C., 35° C., 30° C., 25° C., 20° C., 18° C., 15° C., 12°C., or 10° C. (e.g., from 2 to 40° C., from 5 to 40° C., from 8 to 20°C., from 8 to 18° C., or from 8 to 12° C.).

In some embodiments, step (c) includes the step of forming a mixture inwhich at least 50%, 60%, 70%, 80%, 90%, or 95% (e.g., from 50-55%, from55-60%, from 60-65%, from 65-70%, from 70-75%, from 75-80%, from 80-85%,from 85-90%, from 90-95%, from 95-99%, or from 98-99%) of the compoundof formula (I) relative to the final amount of the compound of formula(I) produced is precipitated.

In some embodiments, step (c) includes the precipitation of at least50%, 60%, 70%, 80%, 90%, or 95% (e.g., from 50-55%, from 55-60%, from60-65%, from 65-70%, from 70-75%, from 75-80%, from 80-85%, from 85-90%,from 90-95%, from 95-99%, or from 98-99%) of the compound of formula (I)relative to the final amount of the compound of formula (I) produced.

In some embodiments, the second composition can include a solution ofthe salt of choline dissolved in a mixture of acetonitrile andtrifluoroacetic acid (TFA), optionally with one or more additionalorganic acids. For example, the additional organic acid that may be usedin combination with acetonitrile and TFA can be methanesulfonic acid oracetic acid. In some embodiments, the second composition can include asolution of the salt of choline dissolved in a mixture of acetonitrileand acetic acid. In some embodiments, the second composition can includea solution of the salt of choline dissolved in a mixture of acetonitrileand methanesulfonic acid. In some embodiments, the second compositioncan include a solution of the salt of choline dissolved in a mixture ofacetonitrile and trifluoromethanesulfonic acid. In particularembodiments, the second composition further includes trifluoroaceticanhydride. In some embodiments, the second composition contains from0.1% to 5% (w/w) water. In some embodiments, the second composition isan anhydrous solution, or the second composition is a mixture comprisingone or more anhydrous solvents.

This invention features a method of synthesizing compound 1, the methodincluding the steps of: (a) providing a first composition including anarylboronate ester of anidulafungin; (b) providing a second compositionincluding a salt of choline; (c) combining the first composition, thesecond composition, and an acid to form a mixture including a compoundof formula (II):

where X⁻ is an anion; and Ar is substituted or unsubstituted C₆ aryl;and (d) hydrolyzing the compound of formula (II) to form compound 1, ora salt or neutral form thereof.

In some embodiments, Ar is phenyl, 3,4-dimethoxyphenyl,4-trifluoromethylphenyl, or 2,6-dimethylphenyl. In some embodiments, Aris phenyl. In some embodiments, Ar is 3,4-dimethoxyphenyl. In otherembodiments, Ar is 4-trifluoromethylphenyl. In still other embodiments,Ar is 2,6-dimethylphenyl.

In certain embodiments of the method, step (c) includes combining atleast 10, 15, 20, 25, 30, 35, or 40 molar equivalents (e.g., from 10 to80, from 10 to 40, from 20 to 60, or from 20 to 40 equivalents) of thesalt of choline with 1 molar equivalent of the3,4-dimethoxyphenylboronate ester of anidulafungin. In certainembodiments of the method, step (c) includes combining at least 10, 15,20, 25, 30, 35, or 40 molar equivalents (e.g., from 10 to 80, from 10 to40, from 20 to 60, or from 20 to 40 equivalents) of the salt of cholinewith 1 molar equivalent of the 4-trifluoromethylphenylboronate ester ofanidulafungin. In certain embodiments of the method, step (c) includescombining at least 10, 15, 20, 25, 30, 35, or 40 molar equivalents(e.g., from 10 to 80, from 10 to 40, from 20 to 60, or from 20 to 40equivalents) of the salt of choline with 1 molar equivalent of the2,6-dimethylphenylboronate ester of anidulafungin.

In some embodiments, the first composition includes a solution of the3,4-dimethoxyphenylboronate ester of anidulafungin dissolved in anorganic solvent selected from acetonitrile, tetrahydrofuran,2-methyltetrahydrofuran, 1,2-dimethoxyethane, cyclopentylmethyl ether,tert-butyl methyl ether, or mixtures thereof. In some embodiments, thefirst composition includes a solution of the4-trifluoromethylphenylboronate ester of anidulafungin dissolved in anorganic solvent selected from acetonitrile, butyronitrile,tetrahydrofuran, 2-methyltetrahydrofuran, 1,2-dimethoxyethane,cyclopentylmethyl ether, tert-butyl methyl ether or mixtures thereof. Insome embodiments, the first composition includes a solution of the2,6-dimethylphenylboronate ester of anidulafungin dissolved in anorganic solvent selected from acetonitrile, butyronitrile,tetrahydrofuran, 2-methyltetrahydrofuran, 1,2-dimethoxyethane,cyclopentylmethyl ether, tert-butyl methyl ether or mixtures thereof. Insome embodiments, the organic solvent contains from 0.1% to 5% (w/w)water. In some embodiments, the organic solvent is anhydrous.

In some embodiments, the second composition can include a solution ofthe salt of choline dissolved in a mixture of acetonitrile andtrifluoroacetic acid (TFA). In particular embodiments, the secondcomposition includes a solution of the salt of choline dissolved in amixture of acetonitrile, trifluoroacetic acid, and trifluoroaceticanhydride. The second composition can include a solution of the salt ofcholine dissolved in a mixture of acetonitrile and acetic acid. Inparticular embodiments, the second composition includes a solution ofthe salt of choline dissolved in a mixture of acetonitrile,trifluoroacetic acid, and acetic acid. The second composition caninclude a solution of the salt of choline dissolved in a mixture ofacetonitrile and methanesulfonic acid.

The second composition can include a solution of the salt of cholinedissolved in a mixture of acetonitrile and trifluoromethanesulfonicacid. In particular embodiments, the second composition further includestrifluoroacetic anhydride. In some embodiments, the second compositioncontains from 0.1% to 5% (w/w) water. In some embodiments, the secondcomposition is anhydrous, or the second composition is a mixture of oneor more anhydrous solvents.

In a particular embodiment of any of the above methods, step (c) furtherincludes the step of adding acetonitrile to the mixture to reduce thelevel of compound 1 beta-diastereomer.

In some embodiments of any of the above methods the mixture is formed ata temperature of less than 40° C., 35° C., 30° C., 25° C., 20° C., 18°C., 15° C., 12° C., or 10° C. (e.g., from 2 to 40° C., from 5 to 40° C.,from 8 to 20° C., from 8 to 18° C., or from 8 to 12° C.).

In some embodiments, step (c) further comprises diluting with at least5, 6, 7, 8, 9, or 10 volumes relative to anidulafungin of water or amixture of water with acetonitrile. In some embodiments, step (c)further comprises diluting with at least 10, 11, 12, 13, 14, or 15volumes relative to anidulafungin of water or a mixture of water withacetonitrile. In some embodiments, step (c) further comprises dilutingwith at least 15, 20, 25, 30, 35, 40, 45, or 50 volumes relative toanidulafungin of water or a mixture of water with acetonitrile.

In some embodiments, the mixture of water with acetonitrile includes atleast 5%, 10%, 15%, 20%, 25%, or 30% water. In some embodiments, themixture of water with acetonitrile includes at least 30%, 35%, 40%, 45%,or 50% water. In some embodiments, the mixture of water withacetonitrile includes at least 50%, 55%, 60%, 65%, or 70% water. In someembodiments, the mixture of water with acetonitrile includes at least70%, 75%, 80%, 85%, 90%, or 95% water.

In some embodiments, step (d) further comprises addition of base toadjust the pH to at least 2 (e.g., from 2 to 3, from 2 to 4, or from 2to 5). In particular embodiments, step (d) includes diluting with atleast 5 volumes relative to anidulafungin of water:acetonitrile mixtureof about 80:20 to 50:50 and adjusting the pH with base to a pH of from 2to 5.

In some embodiments, the base is ammonium acetate, ammonium hydroxide,or ammonium carbonate. In some embodiments, the base is ammoniumacetate. In some embodiments, the base is ammonium hydroxide. In someembodiments, the base is ammonium carbonate.

In a particular embodiment of any of the above methods, step (d)includes forming a reaction product including greater than 70%, 75%,80%, 85%, 88%, or 90% (e.g., from 70% to 95%, from 75% to 90%, from 80%to 90%, or from 85% to 90%) compound 1 (as measured by HPLC) and lessthan 5%, 4%, 3.5%, 3.0%, 2.5%, 2.0%, 1.5% or 1.0% (e.g., from 0% to 1%,from 0% to 2%, from 0% to 3%, from 1.0% to 4.0%, from 1.0% to 3.0%, from1.5% to 3.5%, or from 2.0% to 3.0%) compound 1 beta-diastereomer (asmeasured by HPLC). For example, step (d) can include forming a reactionproduct including greater than 75% compound 1 (as measured by HPLC),less than 2% compound 1 beta-diastereomer (as measured by HPLC), and,optionally, less than 1% (e.g., from 0% to 0.5%, from 0.5% to 1.0% orfrom 0.7% to 1.0%) compound 1 epimer (as measured by HPLC). In someembodiments, step (d) includes forming a reaction product including from75% to 90% compound 1 (as measured by HPLC) and from 1.5% to 3.5%compound 1 beta-diastereomer (as measured by HPLC). In some embodiments,step (d) includes forming a reaction product including from 75% to 90%compound 1 and from 0.5% to 2.5% compound 1 beta-diastereomer. In otherembodiments, step (d) includes forming a reaction product including from75% to 90% compound 1 (as measured by HPLC), from 1.5% to 3.5% compound1 beta-diastereomer (as measured by HPLC), and from 0.5% to 1.0%compound 1 epimer (as measured by HPLC). In other embodiments, step (d)includes forming a reaction product including from 75% to 90% compound1, from 0.5% to 2.5% compound 1 beta-diastereomer, and from 0.1% to 1.0%compound 1 epimer. In a related aspect, the invention features a methodof synthesizing compound 1, the method including: hydrolyzing a compoundof formula (IIa):

wherein X⁻ is an anion, to form compound 1, or a salt or neutral formthereof.

In any of the above methods, the hydrolyzing can include contacting thecompound of any one of formulas (I), (II), (IIa), (IIb), or (IIc) with abase.

In some embodiments, the base is an aqueous base. In particularembodiments, the hydrolyzing is performed at a temperature of less than15° C., 12° C., 10° C., or 8° C. (e.g., from 2 to 15° C., from 5 to 15°C., from 5 to 12° C., from 5 to 10° C., or from 2 to 10° C.).

In particular embodiments, the hydrolyzing comprises diluting with atleast 5 volumes relative to anidulafungin of water:acetonitrile mixtureof about 80:20 to 50:50 and adjusting the pH with base to a pH of from 2to 5.

In any of the above methods, after hydrolyzing the compound of formula(IIa) to form compound 1, or a salt or neutral form thereof, compound 1,or a salt or neutral form thereof, can be separated from3,4-dimethoxyphenylboronic acid by passage across an ion exchange columnor by preparative HPLC.

In any of the above methods, after hydrolyzing the compound of formula(IIb) to form compound 1, or a salt or neutral form thereof, compound 1,or a salt or neutral form thereof, can be separated from4-trifluoromethylphenylboronic acid by passage across an ion exchangecolumn or by preparative HPLC.

In any of the above methods, after hydrolyzing the compound of formula(IIc) to form compound 1, or a salt or neutral form thereof, compound 1,or a salt or neutral form thereof, can be separated from2,6-dimethylphenylboronic acid by passage across an ion exchange columnor by preparative HPLC.

In other embodiments, hydrolyzing to form compound 1 is performed on ascale that produces from 100 grams to 50 Kg of compound 1 (e.g., 100-200grams, 200-500 grams, 500-1000 grams, 1-5 kg, 5-10 kg, 10-20 kg, 20-40kg, or 30-50 kg).

In any of the above methods, the method can further include producing apharmaceutical composition by combining the compound 1, or a salt orneutral form thereof, with pharmaceutically acceptable excipients (e.g.,any excipient described herein). For example, the pharmaceuticalcomposition can be formulated for topical or parenteral administration,or any form of administration described herein.

In a related aspect, the invention features a compound of formula (IIa):

where X⁻ is an anion.

In another aspect, the invention features a compound of formula (IIb):

where X⁻ is an anion.

In yet another aspect, the invention features a compound of formula(IIc):

where X⁻ is an anion.

In another aspect, the invention features a pharmaceutical compositionincluding compound 1, or a salt or neutral form thereof, and apharmaceutically acceptable excipient, wherein the pharmaceuticalcomposition comprises less than 5%, 4%, 3.5%, 3.0%, 2.5%, 2.0%, 1.5% or1.0% (e.g., from 0% to 2.0%, from 0.1% to 4.0%, from 0.75% to 3.0%, from0.5% to 3.5%, or from 1.0% to 3.0%) (w/w) compound 1 beta-diastereomer.In particular embodiments, the pharmaceutical composition also includesless than 1% (e.g., from 0.5% to 1.0% or from 0.7% to 1.0%) (w/w)compound 1 epimer relative to the weight of compound 1, or a salt orneutral form thereof, in the pharmaceutical composition. In someembodiments, the pharmaceutical composition includes from 1.5% to 3.5%(w/w) compound 1 beta-diastereomer and from 0.5% to 1.0% (w/w) compound1 epimer relative to the weight of compound 1, or a salt or neutral formthereof, in the pharmaceutical composition.

Definitions

As used herein, the term “anhydrous solvent system” or “solvent systemis anhydrous” refers to a solvent system that is dried prior to use inthe reaction and/or that contains less than 0.1% of water. For example,“anhydrous acetonitrile” or “acetonitrile is anhydrous” refers toacetonitrile that is dried prior to use in the reaction and/oracetonitrile that contains less than 0.1% of water.

As used herein, the term “compound 1” refers to the compound having thestructure shown below. The term “compound 1 in salt form” or “a salt ofcompound 1” refers to compound 1 when its tertiary ammonium ion positivecharge is balanced with a negative counterion (e.g., an acetate).

As used herein, the term “a neutral form” includes zwitterionic forms ofcompound 1 in which compound 1 has no net positive or negative charge.The zwitterion is present in a higher proportion in basic medium (e.g.,pH of between 7 and 8, between 8 and 9, or between 9 and 10) relative tocompound 1 or a salt of compound 1. In some embodiments, the zwitterionmay also be present in its salt form.

As used herein, the term “compound 1 beta-diastereomer” or“beta-diastereomer” refers to the compound having the structure shownbelow, and salts thereof.

As used herein, the term “compound 1 epimer” or “epimer” refers to thecompound having the structure shown below, and salts thereof.

As used herein, the term “arylboronate ester of anidulafungin” refers tothe compound having the structure shown below, and salts thereof.

where Ar is a substituted or unsubstituted C₆ aryl group.

As used herein, the term “echinocandin-containing” refers to compound 1,compound 1 beta-diastereomer, and/or compound 1 epimer. For example,“echinocandin-containing reaction product” may refer to a reactionproduct that includes compound 1, compound 1 beta-diastereomer, and/orcompound 1 epimer.

As used herein, the term “about” refers to a range of values that is±10% of specific value. For example, “about 150 mg” includes ±10% of 150mg, or from 135 mg to 165 mg. Such a range performs the desired functionor achieves the desired result. For example, “about” may refer to anamount that is within less than 10% of, within less than 5% of, withinless than 1% of, within less than 0.1% of, and within less than 0.01% ofthe stated amount.

As used herein, the term “between” refers to any quantity within therange indicated and enclosing each of the ends of the range indicated.For example, a pH of between 5 and 7 refers to any quantity within 5 and7, as well as a pH of 5 and a pH of 7.

As used herein, the term “infection” or “fungal infection” is meant amicrobial dysbiosis characterized by overgrowth or colonization of anypart of the body of a human subject by one or more species of fungi(e.g., fungal pathogens or opportunistic pathogens), reduction of whichmay provide benefit to the host. For example, the infection may includethe excessive growth of or colonization by fungal species that arenormally present in or on the body of a human subject, or the infectionmay include colonization by fungal species that are not normally presentin or on the body of a human subject. In some instances, the infectionmay include colonization of a part of the body by a fungus that isindigenous to some parts of the human body (e.g., GI tract) but isdetrimental when found in other parts of the body (e.g., tissues beyondthe GI tract). More generally, an infection can be any situation inwhich the presence of a microbial population(s) is damaging to a hostbody.

As used herein, the term “C₆ aryl” refers to an aromatic radical of 6carbon atoms that is unsubstituted or substituted. Substitutions caninclude halogen, methyl, ethyl, ethoxy, methoxy, fluoromethyl,difluoromethyl, and trifluoromethyl. C₆ aryl groups include, withoutlimitation, phenyl, 3,4-dimethoxyphenyl, 4-trifluoromethylphenyl, and2,6-dimethylphenyl. In some embodiments, a C₆ aryl group is substitutedwith one, two, three, four, or five substituents independently selectedfrom the group consisting of: (1) halo; (2) C₁-C₆ alkoxy; (3) C₁-C₆alkyl (e.g., C₁-C₆ perfluoroalkyl); and (4) C₆-C₁₀ aryl. In someembodiments, each of these groups can be further substituted asdescribed herein.

As used herein, the term “salt” refers to any salt form commonly used inthe pharmaceutical industry. Acid addition salts include organic acids,such as acetic, formic, lactic, palmoic, maleic, citric, cholic acid,capric acid, caprylic acid, lauric acid, glutaric, glucuronic, glyceric,glycocolic, glyoxylic, isocitric, isovaleric, lactic, malic, oxaloacetic, oxalosuccinic, propionic, pyruvic, ascorbic, succinic, benzoic,palmitic, suberic, salicylic, tartaric, methanesulfonic,toluenesulfonic, and trifluoroacetic acids, and inorganic acids, such ashydrochloric acid, hydrobromic acid, sulfuric acid, and phosphoric acid.Representative alkali or alkaline earth metal salts include sodium,lithium, potassium, calcium, and magnesium, among others.

At various places in the present specification, substituents ofcompounds of the present disclosure are disclosed in groups or inranges. It is specifically intended that the present disclosure includeeach and every individual subcombination of the members of such groupsand ranges. For example, the term “C₁-C₆ alkyl” is specifically intendedto individually disclose methyl, ethyl, C₃ alkyl, C₄ alkyl, C₅ alkyl,and C₆ alkyl. Furthermore, where a compound includes a plurality ofpositions at which substitutes are disclosed in groups or in ranges,unless otherwise indicated, the present disclosure is intended to coverindividual compounds and groups of compounds (e.g., genera andsubgenera) containing each and every individual subcombination ofmembers at each position.

The term “alkyl,” as used herein, refers to saturated hydrocarbon groupscontaining from 1 to 20 (e.g., from 1 to 10 or from 1 to 6) carbons. Insome embodiments, an alkyl group is unbranched (i.e., is linear); insome embodiments, an alkyl group is branched. Examples of alkyl groupsinclude, but are not limited to, methyl, ethyl, n- and iso-propyl, n-,sec-, iso- and tert-butyl, and neopentyl. In some embodiments, an alkylgroup is unsubstituted. In some embodiments, an alkyl group issubstituted with one, two, three, four, or five substituentsindependently selected from the group consisting of: (1) halo; (2) C₁-C₆alkoxy; (3) C₁-C₆ perfluoroalkyl; and (4) C₆-C₁₀ aryl. In someembodiments, each of these groups can be further substituted asdescribed herein.

The term “alkenyl,” as used herein, represents monovalent straight orbranched chain groups of, unless otherwise specified, from 2 to 10carbons (e.g., from 2 to 4 or from 2 to 6 carbons) containing one ormore carbon-carbon double bonds. Examples of alkenyl groups include, butare not limited to, ethenyl, 1-propenyl, 2-propenyl,2-methyl-1-propenyl, 1-butenyl, and 2-butenyl. In some embodiments, analkenyl group is unsubstituted. In some embodiments, an alkenyl group issubstituted with one, two, three, four, or five substituentsindependently selected from the group consisting of: (1) halo; (2) C₁-C₆alkoxy; (3) C₁-C₆ alkyl (e.g., C₁-C₆ perfluoroalkyl); and (4) C₆-C₁₀aryl. In some embodiments, each of these groups can be furthersubstituted as described herein.

The term “aryl,” as used herein, represents a mono-, bicyclic, ormulticyclic carbocyclic ring system having one or two aromatic rings.Examples of aryl groups include, but are not limited to, phenyl,naphthyl, 1,2-dihydronaphthyl, 1,2,3,4-tetrahydronaphthyl, anthracenyl,phenanthrenyl, fluorenyl, indanyl, and indenyl. In some embodiments, anaryl group is unsubstituted. In some embodiments, an aryl group issubstituted with one, two, three, four, or five substituentsindependently selected from the group consisting of: (1) halo; (2) C₁-C₆alkoxy; (3) C₁-C₆ alkyl (e.g., C₁-C₆ perfluoroalkyl); and (4) C₆-C₁₀aryl. In some embodiments, each of these groups can be furthersubstituted as described herein. Examples of substitutions include, butare not limited to, halo, methyl, ethyl, ethoxy, methoxy, fluoromethyl,difluoromethyl, and trifluoromethyl.

The term “carbocyclyl,” as used herein, refers to represent monocyclic,bicyclic, or tricyclic non-aromatic ring structure in which the ringsare formed by carbon atoms. Examples of carbocyclyl groups include, butare not limited to, cycloalkyl and cycloalkenyl. In some embodiments, acarbocyclyl group is unsubstituted. In some embodiments, a carbocyclylgroup is substituted with one, two, three, four, or five substituentsindependently selected from the group consisting of: (1) halo; (2) C₁-C₆alkoxy; (3) C₁-C₆ alkyl (e.g., C₁-C₆ perfluoroalkyl); and (4) C₆-C₁₀aryl. In some embodiments, each of these groups can be furthersubstituted as described herein.

The terms “halo” or “halogen,” as used herein, refer to a fluorine(fluoro), chlorine (chloro), bromine (bromo), or iodine (iodo) radical.

The term “heteroaryl,” as used herein, represents that subset ofheterocyclyls, as defined herein, which are aromatic: i.e., they contain4n+2 pi electrons within the mono- or multicyclic ring system. Exemplaryunsubstituted heteroaryl groups are of 1 to 12 (e.g., 1 to 11, 1 to 10,1 to 9, 2 to 12, 2 to 11, 2 to 10, or 2 to 9) carbons. In someembodiments, a heteroaryl group is unsubstituted. In some embodiments, aheteroaryl group is substituted with one, two, three, four, or fivesubstituents independently selected from the group consisting of: (1)halo; (2) C₁-C₆ alkoxy; (3) C₁-C₆ alkyl (e.g., C₁-C₆ perfluoroalkyl);and (4) C₆-C₁₀ aryl. In some embodiments, each of these groups can befurther substituted as described herein.

The term “heterocyclyl,” as used herein, represents a 5-, 6- or7-membered ring, unless otherwise specified, containing one, two, three,or four heteroatoms independently selected from the group consisting ofnitrogen, oxygen, and sulfur. In some embodiments, a heterocyclyl groupis unsubstituted. In some embodiments, a heterocyclyl group issubstituted with one, two, three, four, or five substituentsindependently selected from the group consisting of: (1) halo; (2) C₁-C₆alkoxy; (3) C₁-C₆ alkyl (e.g., C₁-C₆ perfluoroalkyl); and (4) C₆-C₁₀aryl. In some embodiments, each of these groups can be furthersubstituted as described herein.

Other features and advantages of the invention will be apparent from thefollowing detailed description and the claims.

DETAILED DESCRIPTION

Provided herein are synthetic methods and intermediates for making theechinocandin antifungal agent compound 1, or a salt or neutral formthereof. The methods and intermediates can be useful for achieving ahigher yield, a higher chemical purity, and/or a higher diastereomericpurity, and a lower cost for the preparation of compound 1. Furthersynthetic details are provided in the Examples.

The invention features a process for synthesis of compound 1 acetatefrom anidulafungin using aryl boronic acids as an in situ protectinggroup, which was developed as follows. In one embodiment, the first stepinvolves slurrying of choline chloride in 2-methyltetrahydrofuran, whichis then distilled off. The resulting solid is further dried in a vacuumoven at elevated temperature. The second step involves protecting theanidulafungin starting material by converting it into its3,4-dimethoxyphenylboronate ester by reacting with 1.3 equivalents of3,4-dimethoxyphenylboronic acid in tetrahydrofuran. Evaporation of thesolvent under reduced vacuum affords the protected intermediate as asolid which is further dried by repeated azeodrying cycles with2-methyltetrahydrofuran. Alternatively, other methods of water removalcan be employed, such as addition of activated molecular sieves,continuous distillation, or addition of dehydrating agents. In the thirdand final step to the crude material, the azeodried choline chloride isdissolved in a mixture of TFA and acetonitrile and conjugated to theprotected anidulafungin backbone to afford the compound 1 as itsTFA/chloride form. The reaction is then quenched by addition of awater:acetonitrile mixture and the pH is adjusted to afford a reasonablystable crude mixture that is ready to be fed into the purificationprocess.

The invention features a process for the synthesis of compound 1 acetatefrom anidulafungin, which entails using 3,4-dimethoxyphenyl boronic acidas an in situ protecting group, wherein, when the conjugation reactionis complete, additional acetonitrile (20 to 50 volumes relative toanidulafungin) is added. This causes precipitation of compound 1. Sincethe equilibrium between compound 1 and the beta-isomer of 1(approximately 95:5) in solution is maintained under the acidicconditions, the precipitation of compound 1 from solution results indriving formation of compound 1 and lowering the beta-isomer amount. Thebeta isomer at the end of reaction can be controlled to no more than2.0% under these conditions.

The invention features a process for the synthesis of compound 1 acetatefrom anidulafungin using 3,4-dimethoxyphenyl boronic acid as an in situprotecting group involves conducting the conjugation reaction with 12-18equivalents of choline chloride under more concentrated conditions. Thiscauses precipitation of compound 1 as the reaction proceeds. Since theequilibrium between compound 1 and the beta-isomer of 1 (approximately95:5) is solution is maintained under the acidic conditions, theprecipitation of compound 1 from solution results in driving formationof compound 1 and lowering the beta-isomer amount. The beta isomer atthe end of reaction can be controlled to less than 2.0% under theseconditions. The invention also features a process for synthesis ofcompound 1 acetate from anidulafungin using 2,6-dimethylphenyl boronicacid as an in situ protecting agent.

The invention also features a process for synthesis of compound 1acetate from anidulafungin using 4-trifluromethylphenyl boronic acid asan in situ protecting agent.

The invention features a purification process where the crude reactionis purified either by reverse phase preparative high performance liquidchromatography (RP-HPLC) or reverse phase preparative medium pressureliquid chromatography (RP-MPLC). The final product can be isolated bylyophilization.

The advantages of the invention include a significant improvement indiastereomeric purity, which allows for a more straightforwardpurification process and an overall higher purity product. Although theboronic acid group is far from the reacting center, it was surprisinglyfound that the nature of the groups on the aryl boronic acid had asignificant impact on the diastereoselectivity in the conjugationreaction. In particular, the use of the 3,4-dimethoxyphenylboronateester of anidulafungin reduced the amount of compound 1beta-diastereomer formed relative to other boronate esters, resulting ina simpler purification method and higher purity of compound 1.

Compound 1 can be useful for treating, mitigating, or preventing afungal infection or related conditions thereto in a human subject inneed thereof.

Compound 1 may be prepared in a pharmaceutical composition. Thepharmaceutical composition can include a salt of compound 1, or aneutral form thereof, and pharmaceutically acceptable carriers andexcipients. The pharmaceutical composition can be formulated forsubcutaneous injection or intravenous infusion. Depending on the mode ofadministration (e.g., subcutaneously or intravenously) and the dosage,compound 1 may be formulated into suitable pharmaceutical compositionsto permit facile delivery. A summary of such techniques is found inRemington: The Science and Practice of Pharmacy, 22nd Edition,Lippincott Williams & Wilkins, (2012); and Encyclopedia ofPharmaceutical Technology, eds. J. Swarbrick and J. C. Boylan, 2006,Marcel Dekker, New York, each of which is incorporated herein byreference.

For subcutaneous administration, compound 1 may be formulated as anaqueous pharmaceutical composition. In some embodiments, thepharmaceutical composition containing compound 1 formulated forsubcutaneous administration may not contain a buffer. In someembodiments, the pharmaceutical composition formulated for subcutaneousadministration may contain a weak buffer. Examples of a weak buffer thatmay be used in the pharmaceutical composition include, but are notlimited to, acetate, lactate, histidine, glycine, and formate.

A pharmaceutical composition including compound 1 in salt or neutralform may optionally contain an amount of a solubilizing agent. Examplesof a solubilizing agent include, but are not limited to, polysorbate 20(Tween 20; polyoxyethylene (20) sorbitan monolaurate), polysorbate 40(Tween 40; polyoxyethylene (40) sorbitan monopalmitate), polysorbate 60(Tween 60; polyoxyethylene (60) sorbitan monostearate), polysorbate 80(Tween 80; polyoxyethylene (80) sorbitan monooleate), β-cyclodextrin,polyoxyl 35 castor oil (Cremophor EL), polyoxyl 40 hydrogenated castoroil (Cremophor RH 40), polyoxyl 60 hydrogenated castor oil (Cremophor RH60), D-α-tocopheryl polyethylene glycol 1000 succinate (TPGS), sorbitanmonooleate (Span 20), polyoxyl 8 stearate (PEG 400 monosterate),polyoxyl 40 stearate (PEG 1750 monosterate), PEG 400 caprylic/capricglycerides (Labrasol), PEG 300 oleic glycerides (Labrafil M-1944CS),phosphatidylcholine (lecithin), alkylglucoside, sucrose monolaurate,sucrose monooleate, and polyoxyethylene-polyoxypropylene block copolymer(Poloxamer).

Furthermore, a pharmaceutical composition including compound 1 in saltor neutral form may contain between 0.5% to 3% (w/w) of a saccharide.Examples of a saccharide that may be included in the pharmaceuticalcomposition including compound 1 in salt or neutral form used in themethods of the invention include, but are not limited to, mannitol,sucrose, trehalose, fructose, glucose, dextrose, dextran, lactose, andsorbital.

A pharmaceutical composition including compound 1 in salt or neutralform may be formulated as a lyophilized composition. Moreover, thelyophilized composition including compound 1, when re-constituted inwater for injection, may have a pH of between 5 and 6.5 (e.g., about 5,about 5.3, about 5.6, about 5.9, about 6.2, or about 6.5). In someembodiments, compound 1 in salt form may be compound 1 acetate.

The pharmaceutical compositions used in methods of the invention may beformulated in the form of liquid solutions or suspensions or lyophilizedcakes and administered by a parenteral route (e.g., subcutaneous orintravenous). Pharmaceutical compositions for parenteral administrationcan be formulated using a sterile solution or any pharmaceuticallyacceptable liquid as a vehicle. Pharmaceutically acceptable vehiclesinclude, but are not limited to, sterile water, physiological saline, orcell culture media (e.g., Dulbecco's Modified Eagle Medium (DMEM),α-Modified Eagles Medium (α-MEM), F-12 medium). Formulation methods areknown in the art, see e.g., Gibson (ed.) Pharmaceutical Preformulationand Formulation (2nd ed.) Taylor & Francis Group, CRC Press (2009).

Furthermore, acceptable carriers and excipients in the pharmaceuticalcomposition used in methods of the invention are nontoxic to recipientsat the dosages and concentrations employed. Acceptable carriers andexcipients may include buffers such as phosphate, citrate, histidine,HEPES, and TAE, antioxidants such as ascorbic acid and methionine,preservatives such as hexamethonium chloride, octadecyldimethylbenzylammonium chloride, resorcinol, and benzalkonium chloride, proteins suchas human serum albumin, gelatin, dextran, and immunoglobulins,hydrophilic polymers such as polyvinylpyrrolidone, amino acids such asglycine, glutamine, histidine, and lysine, and carbohydrates such asglucose, mannose, sucrose, and sorbitol. The compositions may beformulated according to conventional pharmaceutical practice. Theconcentration of the compound in the formulation will vary dependingupon a number of factors, including the dosage of the drug to beadministered, and the route of administration.

The pharmaceutical compositions of the invention can be administered tohuman subjects in therapeutically effective amounts. The preferreddosage of drug to be administered is likely to depend on such variablesas the type and extent of the disorder, the overall health status of theparticular human subject, the specific compound being administered, theexcipients used to formulate the compound, and its route ofadministration.

The timing of the administration of the pharmaceutical compositioncontaining compound 1 in salt or neutral form depends on the medical andhealth status of the human subject. In some instances, the human subjectis at risk for developing a fungal infection or a related condition andreceives one or more doses treatment with compound 1 before developingsymptoms or signs of a fungal infection. In some instances, the humansubject has already developed a fungal infection or a related conditionand receives one or more doses treatment with compound 1. The timing ofthe administration of the dose(s) of compound 1 may be optimized by aphysician to reduce the risk of or to treat a fungal infection in ahuman subject.

The following examples, as set forth below, are put forth so as toprovide those of ordinary skill in the art with a complete disclosureand description of how the methods and compounds claimed herein areperformed, made, and evaluated, and are intended to be purely exemplaryof the invention and are not intended to limit the scope of what theinventors regard as their invention.

EXAMPLES Example 1. Synthesis of Compound 1 from the phenylboronateEster of Anidulafungin

Anidulafungin phenylboronate ester:

To a solution of anidulafungin (5 g) in tetrahydrofuran (70 mL) wasadded a solution of phenylboronic acid (0.7 g) in tetrahydrofuran (30mL). The reaction mixture was stirred at room temperature for 90minutes. The reaction mixture was concentrated by rotary evaporation.The resulting solid was dissolved in tetrahydrofuran (60 mL) andconcentrated by rotary evaporation. The resulting solid was againdissolved in tetrahydrofuran (60 mL) and concentrated by rotaryevaporation. The resulting solid mixture was re-dissolved inacetonitrile/tetrahydrofuran (30 mL/15 mL) and concentrated by rotaryevaporation. The resulting anidulafungin phenylboronate ester solid wasdried in vacuum overnight.

Choline Chloride Drying:

In a round bottom flask choline chloride (18.6 g) was suspended inacetonitrile (150 mL) and stirred for 4 hours. The suspension wasconcentrated by rotary evaporation. The choline chloride was suspendedin acetonitrile (150 mL) and concentrated by rotary evaporation, andthis step was repeated one more time. The resulting solid was driedovernight in vacuum.

Conjugation:

In a round bottom flask, the dried choline chloride was dissolved inacetonitrile (50 mL) and trifluoroacetic acid (TFA) (12.5 mL). Theresulting choline chloride solution was added to the dried anidulafunginphenylboronate ester. The resulting reaction mixture was stirred at roomtemperature for 2.5 hours. The reaction was quenched by the addition ofwater (125 mL) and was basified with NH₄OH (2N, ˜40 mL) to pH ˜2. Awhite material was formed and was dissolved with acetonitrile (300 mL).The material contained 4.55% compound 1 beta-diastereomer (average oftwo runs).

Purification:

The material was purified by preparative reversed-phase HPLC with C18silica media using Buffer A (0.1% TFA in water) and Buffer B (0.1% TFAin 50% acetonitrile/50% water). The product was eluted using a 90 minutegradient starting with 70% B/30% A to 100% B. Pools resulting from thefinal purification were lyophilized to obtain the dried final bulk drugsubstance (2.9 g isolated compound 1).

Example 2. Synthesis of Compound 1 from the4-(trifluoromethyl)phenylboronate Ester of Anidulafungin

The reaction was carried out on 200 mg scale similar to the process ofExample 1 except for the change in boronic acid to4-(trifluoromethy)phenylboronic acid and a reaction time of 24 hours.Results: 63% compound 1; 7.0% compound 1 beta-diastereomer.

A second conjugation experiment was performed where the4-(trifluoromethyl)phenylboronate ester was solubilized inacetonitrile:TFA mixture initially, and then the dried choline chloridesolution was added to it. After 2.5 h the reaction mixture was dilutedwith water:acetonitrile (70:30) and the pH was adjusted to 2.0 byaddition of ammonium hydroxide. Results: 75% compound 1; 4.8% compound 1beta-diastereomer.

Example 3. Synthesis of Compound 1 from the 2,6-dimethylphenylboronateEster of Anidulafungin

The reaction was carried out on 200 mg scale similar to the process ofExample 1 except for the change to the boronic acid to2,6-dimethylphenylboronic acid. Results: 55% compound 1; 7.4% compound 1beta-diastereomer.

Example 4. Synthesis of Compound 1 from the 3,4-dimethoxyphenylboronateEster of Anidulafungin

The reactions were carried out on 200 mg scale similar to the process ofExample 1 except for the replacing the boronic acid to3,4-dimethoxyphenylboronic acid. Runs 1-3 were carried out to establishreproducibility of the process. Run 4 was performed with 10 equivalentsof choline chloride (rather than the 30 equivalents used in Example 1).Run 5 was performed at 40° C. (rather than at room temperature asdescribed in Example 1). Results are provided in Table 1 below.

TABLE 1 Run No. Compound 1 Beta-diastereomer 1 88.8% 2.6% 2 86.4% 3.7% 386.4% 3.0% 4 78.8% 3.4% 5 88.4% 4.0%

The use of the 3,4-dimethoxyphenylboronate ester of anidulafunginreduced the amount of compound 1 beta-diastereomer formed relative toother boronate esters.

Example 5. Synthesis of Compound 1 from the 3,4-dimethoxyphenylboronateEster of Anidulafungin Made from a Stoichiometric Amount of3,4-dimethoxyphenylboronic Acid

The effect of using a stoichiometric amount (1.05 eq) of3,4-dimethoxyphenylboronic acid in the conjugation step wasinvestigated. The reaction was performed on a 500 mg anidulafungin inputand performed as previously described in Example 1 except for thereplacing the boronic acid to 3,4-dimethoxyphenylboronic acid. Resultsare provided in Table 2 below.

TABLE 2 Boronic compound compound 1 beta- unreacted compound 1 acid (eq)1 diastereomer anidulafungin epimer 1.3 89.5% 2.5% 5.7% 0.5% 1.05 89.4%2.0% 4.2% 1.3%

We can conclude from these data that while using a stoichiometric amountof boronic acid in the process may lead to a further reduction in thefraction of compound 1 beta-diastereomer that is generated, the amountof compound 1 epimer byproduct, on the other hand, is significantlyincreased.

Example 6. Synthesis of Compound 1 from the 3,4-dimethoxyphenylboronateEster of Anidulafungin

Choline chloride drying:

Choline chloride (185 g) was suspended in 2-methyltetrahydrofuran (500ml) and stirred for 1 hour at room temperature. The solvent was removedunder vacuum to near-dryness then dried under vacuum at 70-75° C. for 1hour.

Anidulafungin boronate ester preparation:

Anidulafungin (50 g), 3,4-dimethoxyphenylboronic acid (10.37 g), andtetrahydrofuran (250 ml) were charged in a 1000 mL round bottom flask.The suspension was stirred at room temperature for 1.5 hours. Thesolvent was removed under vacuum. The resulting solid was solubilized in2-methyltetrahydrofuran (400 mL) and the solvent was evaporated undervacuum. This process was repeated one more time.

Conjugation:

Dried choline chloride (73.6 g), acetonitrile (200 mL) andtrifluoroacetic acid (48 mL) were combined. The suspension was stirredfor 10 min. In a second reactor, dried anidulafungin boronate ester(25.6 g) and dry tetrahydrofuran (150 mL) were combined and stirred atroom temperature until the material was completely solubilized (30minutes). The acidic solution of choline chloride was added to thestirred boronate ester solution over 30 minutes. The resultingsuspension was stirred for 3 hours at room temperature then cooled to≤10° C. and quenched by addition of 70/30 water:acetonitrile mixture(560 mL). The pH of the crude reaction mixture was adjusted within the2.0-2.2 range by slow addition of chilled half-dilute ammonium hydroxidesolution (typically 80-82 mL). The crude solution was diluted to a finalvolume of 2000 mL with 70/30 water:acetonitrile solution. The compound 1beta-diastereomer content of the crude solution was 3.7% and thecompound 1 epimer content was 0.43%.

After synthesis of the crude mixture, compound 1 was purified using areversed phase C18 silica media, with the product eluted from the columnusing an aqueous acetonitrile gradient. A formal acetate exchange andremoval of boronic acid was performed in the same process. Final poolsof the appropriate purity were brought forward to an on-columnconcentration using the same media to generate a concentrated solution.Post concentration, compound 1 solution was concentrated viaacetonitrile removal under reduced pressure; the concentrated solutionwas filtered through a 0.2 μm filter and freeze-dried to producecompound 1 acetate as a white solid with 97.7% purity, 1.6% compound 1beta-diastereomer, and 0.43% compound 1 epimer.

Example 7. Synthesis of Compound 1 from the 3,4-dimethoxyphenylboronateEster of Anidulafungin—Effect of Dilution with Acetonitrile

The boronate ester was prepared and coupled with choline chloride inacetonitrile using the conditions reported in example 6. The reactionwas complete in 2-3 hours and formed a approx. 96:4 mixture of compound1:compound 1 beta-diastereomer. This ratio was improved to >98:2 bydilution of the reaction mixture with additional acetonitrile (20-50volumes relative to anidulafungin) at the end of the reaction, whichprecipitates the alpha isomer and results in conversion of beta to alphaisomer. The reaction was then quenched with aqueous ammonia/ammoniumacetate to pH 4. The crude yield of compound 1 trifluoroacetate was75-80%.

Example 8. Synthesis of Compound 1 from the 3,4-dimethoxyphenylboronateEster of Anidulafungin—Combination of TFAA and Dilution withAcetonitrile

Boronate ester slurry synthesis:

To a 1000 mL reactor the following were charged: tetrahydrofuran (250mL), anidulafungin (25 g), 3,4-dimethoxyphenylboronic acid (5.25 g). Thesuspension was stirred for 1 h at room temperature. The jackettemperature was set to 30-35° C., a vacuum applied, and tetrahydrofurandistillation was initiated. Portion wise (62.5 mL) additions oftetrahydrofuran were made to maintain a constant volume in the reactorwhile distilling. A total of 1250 mL of tetrahydrofuran was distilled.Then, acetonitrile (500 mL) was charged and distilling re-initiated.Approximately 600 mL of tetrahydrofuran/acetonitrile mixture weredistilled. Additional acetonitrile (250 mL) was charged and 250 mL ofacetonitrile/tetrahydrofuran mixture distilled under vacuum. The reactorcontents were cooled to 18-22° C.

Acidic choline chloride solution makeup:

Acetonitrile (57.5 mL), choline chloride (52.5 g), trifluoroacetic acid(32.5 mL) and trifluoroacetic anhydride (2.0 mL) were charged to a 250mL round-bottom flask. The mixture was stirred at 18-22° C. for onehour.

Conjugation:

The acidic choline chloride solution was transferred to the reactorcontaining the slurry of boronate ester. After 1.75 to 2.00 hours postmixing, acetonitrile (285 mL) was added to the reaction mixture andstirred at 10-15° C. for 1 hour. Additional acetonitrile (285 mL) wasthen added. If the % compound 1 beta-diastereomer was >2.0%, additionalacetonitrile (142 mL) was added. After 0.5 hours, the reaction wasquenched by adding chilled ammonium acetate solution (143 mL) followedby slow addition of a chilled solution of 9M aqueous ammonium hydroxide(28.7 mL) so as to maintain a temperature <15° C. and bring the pHwithin a range of 4.0-4.7. The crude yield of compound 1trifluoroacetate was 75-80% with less than 2% compound 1beta-diastereomer.

Example 9. Synthesis of Compound 1 from the 3,4-dimethoxyphenylboronateEster of Anidulafungin—Coupling in the Presence of TFAA

Tetrahydrofuran (700 mL) and anidulafungin (108.44 g) were charged to a1 L reactor. 3,4-Dimethoxyphenylboronic acid (21.0 g) was then chargedand the mixture was stirred at 18-22° C. The reaction mixture wasazeodried by distillation of tetrahydrofuran and simultaneous additionof fresh tetrahydrofuran (7.0 L). A constant volume solvent swap toacetonitrile was carried out by addition of acetonitrile (2.1 L) andsimultaneous vacuum distillation. After complete turnover toacetonitrile, further distillation was carried out to reduce the volumeto 420 mL.

In a separate vessel, the following were combined with stirring: cholinechloride (172 g), acetonitrile (217 mL), trifluoroacetic acid (142 mL),and trifluoroacetic anhydride (8.6 mL). This solution was then added tothe slurry containing the anidulafungin boronate ester and the resultingmixture was stirred at 15° C. for 8 hours. The reaction was quenched bycharging cooled (T<10° C.) solution of ammonium acetate (4.2 M, 221 mL)to the reactor at once followed by addition of chilled (T<10° C.)) water(221 mL). Then, a cooled (10° C.) solution of ammonium hydroxide (9.0 M,126.4 mL) was added. The final pH was adjusted to pH 4.0-4.6 by additionof ammonium hydroxide. The crude reaction mixture was diluted withwater:acetonitrile (3:1, 6 L) and stored at −20° C.

Results: compound 1, 76.8%, compound 1 beta-diastereomer, 0.8%.

A reduction in the level of compound 1 beta-diastereomer has allowed forreplacement of the HPLC purification with medium pressure chromatography(MPLC) using a coarser grade of C18 silica (25 to 50 μm). The3,4-dimethoxyphenyl boronic acid can be separated by ion-exchangecapture, eluting with 100 mM ammonium acetate (pH 4.5) inwater:acetonitrile 50:50 v:v, which affords salt exchange fromtrifluoroacetate to acetate.

Post chromatography, the compound 1 acetate solution was concentrated byvacuum distillation to remove the majority of acetonitrile. Theconcentrated solution was filtered through a 0.2 μm filter andfreeze-dried to produce compound 1 acetate. The purity after MPLC andafter ion exchange and lyophilization is provided in Table 3 below.

TABLE 3 compound 1 beta- compound 1 Stage compound 1 diastereomer epimerafter MPLC 98.47% 0.77% 0.47% after ion exchange and 98.49% 0.77% 0.51%lyophilization

Other Embodiments

All publications, patents, and patent applications mentioned in thisspecification are herein incorporated by reference to the same extent asif each independent publication or patent application was specificallyand individually indicated to be incorporated by reference.

While the disclosure has been described in connection with specificembodiments thereof, it will be understood that it is capable of furthermodifications and this application is intended to cover any variations,uses, or adaptations of the disclosure following, in general, theprinciples of the disclosure and including such departures from thepresent disclosure that come within known or customary practice withinthe art to which the disclosure pertains and may be applied to theessential features hereinbefore set forth, and follows in the scope ofthe claims. Other embodiments are within the claims.

What is claimed is:
 1. A method of synthesizing compound 1:

said method comprising: (a) providing a first composition comprising aboronate ester of anidulafungin; (b) providing a second compositioncomprising a salt of choline; (c) combining the first composition, thesecond composition, and trifluoroacetic acid in a solvent system thatcomprises acetonitrile and trifluoroacetic anhydride to form aprecipitate of a reaction product having formula (I):

wherein X⁻ is an anion; and R is C₁-C₆ alkyl or C₆-C₁₀ aryl; and; (d)hydrolyzing the compound of formula (I) to form compound 1, or a salt orneutral form thereof.
 2. The method of claim 1, wherein theconcentration of the mixture is at least 0.01 moles per L relative tothe compound of formula (I).
 3. The method of claim 1, wherein step (c)comprises forming a mixture in a solvent system comprising a mixture oftetrahydrofuran and acetonitrile.
 4. The method of claim 1, wherein step(c) comprises forming a mixture comprising at least 10 molar equivalentsof the salt of choline and at least 1 molar equivalents of the boronateester of anidulafungin.
 5. The method of claim 1, wherein step (c) isperformed at a temperature of less than 40° C.
 6. The method of claim 1,wherein step (c) comprises forming a mixture in which at least 50% ofthe compound of formula (I) is precipitated.
 7. The method of claim 1,wherein R is C₆-C₁₀ aryl.
 8. The method of claim 1, wherein R is C₁-C₆alkyl.
 9. A method of synthesizing compound 1:

said method comprising: (a) providing a first composition comprising anaryl boronate ester of anidulafungin; (b) providing a second compositioncomprising a salt of choline; (c) combining the first composition, thesecond composition, and an acid to form a mixture comprising a compoundof formula (II):

wherein X⁻ is an anion; and Ar is substituted C₆ aryl; and (d)hydrolyzing the compound of formula (II) to form compound 1, or salt orneutral form thereof.
 10. The method of claim 9, wherein Ar is selectedfrom 3,4-dimethoxyphenyl, 2,6-dimethylphenyl, and4-trifluoromethylphenyl.
 11. The method of claim 9, wherein step (c)comprises combining at least 10 molar equivalents of the salt of cholinewith at least 1 molar equivalents of the boronate ester ofanidulafungin.
 12. The method of claim 9, wherein the first compositioncomprises a solution of the boronate ester of anidulafungin dissolved inan organic solvent selected from acetonitrile, butyronitrile,tetrahydrofuran, or 2-methyltetrahydrofuran, or a mixture thereof. 13.The method of claim 9, wherein the second composition comprises asolution of the salt of choline dissolved in a mixture of acetonitrileand trifluoroacetic acid.
 14. The method of claim 9, wherein the secondcomposition comprises a solution of the salt of choline dissolved in amixture of acetonitrile, trifluoroacetic acid, and trifluoroaceticanhydride.
 15. The method of claim 9, wherein step (c) further comprisesadding acetonitrile to the mixture to reduce the level ofbeta-diastereomer.
 16. The method of claim 9, wherein step (d) furthercomprises diluting with at least 5 volumes relative to anidulafungin ofwater:acetonitrile mixture of about 80:20 to 50:50 and adjusting the pHwith base to a pH of from 2 to
 5. 17. The method of claim 9, whereinstep (d) comprises forming a reaction product comprising greater than70% compound 1 and less than 4% compound 1 beta-diastereomer.
 18. Themethod of claim 9, wherein the hydrolyzing is performed at a temperatureof less than 15° C.
 19. The method of claim 9, wherein the methodfurther comprises producing a pharmaceutical composition by combiningthe compound 1 with a pharmaceutically acceptable excipient.
 20. Themethod of claim 9, wherein the acid of step (c) is trifluoroacetic acid.21. The method of claim 9, wherein the solvent system of step (c)comprises acetonitrile and trifluoroacetic anhydride.
 22. The method ofclaim 9, wherein the method further comprises the step (e) purifyingcompound 1, or a salt or neutral form thereof, by reverse phasepreparative high performance liquid chromatography or reverse phasepreparative medium pressure liquid chromatography.
 23. The method ofclaim 1, wherein the method further comprises step (e) purifyingcompound 1, or a salt or neutral form thereof, by reverse phasepreparative high performance liquid chromatography or reverse phasepreparative medium pressure liquid chromatography.